Do words like 'viagra' trigger spam filters in email subject lines?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jul 2025
Updated 19 Aug 2025
7 min read
The question of whether specific words, such as 'viagra,' automatically trigger spam filters in email subject lines is a common concern for marketers and senders. While it's true that early spam filters heavily relied on keyword matching, the landscape of email deliverability has evolved significantly. Modern spam filters are far more sophisticated, employing complex algorithms that analyze a multitude of factors beyond just individual words.
Simply including a word like 'viagra' in a subject line doesn't guarantee your email will go to the spam folder. Instead, deliverability depends on a holistic assessment of your sending practices, sender reputation, email content, and recipient engagement. It's a nuanced system where context plays a crucial role.
This evolution means that while certain words might still contribute to a spam score, they are rarely the sole determining factor. Email service providers (ESPs) and internet service providers (ISPs) like Google Outlook Yahoo and others focus on identifying truly unsolicited or malicious email, rather than punishing legitimate senders for using specific terminology in an appropriate context. For more on this, you can look into whether spam trigger words are still relevant for deliverability.
The evolution of spam filters
While historically words like 'viagra' were significant red flags, modern spam filters understand context. An email about a medical study discussing drug prices, even if it mentions 'viagra' or 'cialis', is treated differently from an unsolicited promotional email attempting to sell pharmaceuticals. The key lies in the overall nature and intent of your message.
Reputation is paramount. If your domain has a strong sending reputation, a single 'trigger word' is less likely to cause a problem. Conversely, if your reputation is already low due to past spam complaints, low engagement, or poor sending practices, then such words can compound the issue. Always focus on maintaining a healthy sender reputation to ensure your emails reach the inbox.
Spam filters (also known as content filters or blocklists) analyze various aspects of an email. This includes the sender's IP and domain reputation, email authentication (SPF, DKIM, DMARC), recipient engagement, and the quality and relevance of the content itself. A comprehensive approach to email deliverability is always more effective than simply avoiding a list of 'spam words'.
Old approach (Keyword matching)
Static lists: Filters used pre-defined lists of words considered spammy.
Score-based: Each 'spam word' added points to an email's spam score.
Context ignored: Limited ability to differentiate legitimate usage from spam.
Context over keywords
While avoiding common spam words (or blacklist words) is a good general practice for email marketers, it's not a silver bullet for deliverability. Modern filters consider multiple signals simultaneously. For example, a high volume of emails sent to unengaged recipients, combined with a subject line containing suspicious words, is far more likely to trigger a blocklist (or blacklist) than a single keyword in an otherwise legitimate email.
Think of it this way, spam filters are trying to replicate human judgment. If you received an email from a reputable sender you've interacted with, discussing medical research, you wouldn't mark it as spam just because it contained the word 'viagra'. Spam filters strive to make similar intelligent distinctions. This is why single words in the subject line typically do not hurt delivery.
The focus should be on building and maintaining a strong sender reputation. This includes consistent email authentication, low spam complaint rates, high engagement, and sending relevant content to an opted-in audience. You can find more information on what spam trigger words are and how they impact deliverability. When considering if words like 'viagra' trigger spam filters, remember to evaluate the broader context.
Focus on sender reputation
High sending volume with consistent engagement metrics and strong authentication builds trust with ISPs, minimizing the impact of any single blocklist or blacklist word.
Focus on keywords
Solely avoiding 'spam words' (or blacklist words) without addressing underlying reputation issues will not guarantee inbox delivery. This is a common deliverability pitfall.
Recipient perception and practical testing
While advanced filters are smart, it doesn't mean you should be careless. Deliberately using words associated with spam, even in a legitimate context, can still negatively affect how recipients perceive your email. This can lead to increased spam complaints, which are a major red flag for ISPs and a primary driver of lower inbox placement.
For instance, if your subject line uses all caps, excessive exclamation marks, or misleading phrasing in addition to a word like 'viagra', the combined effect will likely push your email to the spam folder. SpamAssassin, for example, assigns scores to various characteristics, and while no longer a dominant filter, its older rule sets still show how words like 'viagra' were scored.
It's always a good idea to perform A/B testing on subject lines, especially when you're on the fence about certain words. Monitor your open rates, click-through rates, and, most importantly, your spam complaint rates. This data provides real-world insights into how your audience and their email providers react to your messaging.
Subject line best practices
Be clear and concise: Clearly communicate your email's purpose without being overly promotional. For more, see what words to avoid in subject lines.
Avoid excessive punctuation: Limit exclamation marks and dollar signs.
Personalize: Use personalization where appropriate to increase relevance.
Beyond the keyword trap
Modern spam filters are designed to be smarter than simple keyword matching. They analyze an email's sender reputation, authentication, engagement metrics, content quality, and even how it's formatted to determine if it's spam. So, while 'viagra' used to be a surefire way to hit the spam folder, today's systems are much more discerning.
This means that if you're a legitimate sender with a good reputation and your email is relevant to your subscribers, using a word like 'viagra' in a scientific or medical context (e.g., a study on drug pricing) is unlikely to cause an immediate spam classification. The key is that the overall email should not resemble typical spam characteristics.
However, if your sending practices are poor, such as sending to unengaged lists, having high bounce rates, or lacking proper email authentication, then even seemingly innocuous words can contribute to a negative spam score. It's about the entire picture, not just one brushstroke. This is why specific spam words still affect email deliverability, but not in isolation.
Views from the trenches
Best practices
Maintain an excellent sender reputation by sending consistent, valuable content to engaged subscribers.
Implement strong email authentication: SPF, DKIM, and DMARC are crucial for verifying your sending legitimacy.
Segment your audience and personalize content to ensure relevance, reducing spam complaints.
Continuously monitor your deliverability metrics, including open rates, click rates, and spam complaints.
Common pitfalls
Relying solely on lists of 'spam words' (or blocklist words) as your primary deliverability strategy.
Ignoring recipient engagement, which is a major signal to ISPs about the quality of your mail.
Using misleading subject lines or content, regardless of specific keywords, which leads to complaints.
Failing to properly authenticate emails, increasing the likelihood of being flagged as suspicious.
Expert tips
Focus on the holistic health of your email program, not just isolated content elements.
A/B test suspicious subject lines with small, engaged segments to gauge impact.
Clean your email lists regularly to remove unengaged or invalid addresses.
Prioritize providing value to your subscribers to foster positive engagement signals.
Expert view
Expert from Email Geeks says that modern filters from large providers can distinguish between a legitimate study mentioning 'viagra' and an unsolicited offer for knockoff products.
2019-11-18 - Email Geeks
Marketer view
Marketer from Email Geeks says that while one word may not cause spam placement directly, it can still have some weight on the overall decision by spam filters.
2019-11-18 - Email Geeks
The modern approach to spam filtering
The short answer is no, not directly. While words like 'viagra' were once immediate spam triggers, today's email filters are far more sophisticated. They evaluate the entire context of your email, your sender reputation, and recipient engagement rather than relying on a simple keyword blacklist (or blocklist).
However, using such words carelessly, especially in conjunction with other spammy characteristics (like excessive punctuation or misleading claims), can still contribute to a negative spam score or increase spam complaints from recipients. The focus should always be on providing value to your audience and maintaining strong deliverability practices. Understand why your emails fail and how to improve deliverability.
Prioritize building a positive sender reputation through consistent authentication, sending to an engaged audience, and monitoring your email program's performance. By doing so, you can use industry-specific terms with confidence, knowing that modern filters distinguish legitimate content from actual spam.
Google 
Outlook 
Yahoo and others focus on identifying truly unsolicited or malicious email, rather than punishing legitimate senders for using specific terminology in an appropriate context. For more on this, you can look into whether spam trigger words are still relevant for deliverability.
