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There has been a lot of talk over the past several years about an overall decline in sperm counts globally. The research is not definitive on whether this decline is real, and if it is, how large it is or what causes it. Even if sperm counts have gone down, it’s not clear how much that impacts fertility; men produce a lot of sperm at once, and you only need one sperm to fertilize the egg. But whether it is worthy of panic or not, this discussion has put more focus on sperm health and on the male-side factors that drive fertility and may impact infertility.
There are a number of ways to measure sperm health, but the core metrics are count, morphology (the shape), and motility (how well they swim).
Unlike eggs, sperm are continuously regenerated in the testes — the cycle is about 64 days. This means that — again, unlike eggs — sperm health can be impacted by relatively short-term behaviors. One of the most well-known risks to sperm is heat. Tight shorts or underwear, or extensive use of hot tubs and saunas, can impact sperm parameters.
If you are trying to conceive, then it is best to keep your testes relatively cool. But what about other, more complicated behavior changes? You’ll often hear that sperm is impacted by marijuana, alcohol, and smoking. How important are these behaviors in optimizing your sperm health? Let’s go to the data.
Impacts of smoking and nicotine on sperm
There is a lot of evidence that cigarette smoking negatively impacts sperm. This data goes back a long time; a 1981 Lancet piece, for example, reported negative impacts of smoking on sperm morphology. Even among individuals with infertility, smokers are more likely to have abnormal sperm parameters.
These negative impacts also show up in the general population. A 2025 study uses 113 men, including tobacco smokers, non-smokers, and cannabis smokers (more on the latter group below). The study found very large reductions in morphologically normal sperm in the tobacco smoking group. Among non-smokers, about 30% of their sperm were morphologically normal (meaning they had the normal sperm shape). Among tobacco smokers, this was only around 5%. There were also smaller impacts on sperm mobility and concentration.
There is plenty of data on this, and it seems clear that quitting smoking would improve sperm morphology in particular. That’s actually not the biggest benefit of quitting smoking, of course. There are a lot of good reasons not to smoke tobacco.
Although smoking is the most common way people consume nicotine, there is increasing interest in the consumption of nicotine alone for its benefits in focusing. This is most common among a group of men I might refer to as “optimizers.” A number of very popular podcasts have nodded to the possible positive cognitive benefits of nicotine.
The data pretty clearly shows that nicotine has some positive attention and cognitive benefits. Typically, people looking for these benefits are consuming nicotine through gum, a nicotine patch, or Zyn, which is a nicotine pouch. Use of these products is not without risk; they cause elevated heart rate and blood pressure, and nicotine is extremely addictive.
In terms of impacts on sperm, though, the evidence on smoking is not necessarily directly applicable here. Tobacco has many bad components (e.g., nicotine and tar), and it’s hard to know which of them impacts sperm.
We have some evidence that nicotine itself matters for sperm. In rats, treatment with nicotine reduced sperm count and negatively affected sperm morphology. They also showed a reduced libido (so, keep that in mind). Nicotine has also been shown to affect sperm in a lab environment in the same ways.
What we do not have is direct evidence on the sperm of non-smoking nicotine users or, even better, a randomized trial that encouraged some of them to quit and measured sperm before and after. All the data we do have points to negative impacts, but it is worth saying that the data is incomplete.
Impact of cannabis on sperm
In mice, marijuana exposure is linked to infertility. There are biological reasons to think the link might be in people, too. There is a 2021 review that pulls together what we know about marijuana consumption and sperm parameters. It does conclude that marijuana is linked to lower sperm counts and worse sperm quality on basically every metric.
The authors of this review note that the evidence here is limited. One problem is that cannabis use is associated with other lifestyle choices, and it’s hard to isolate cannabis use. A second issue is that sperm quality evaluation is mostly done as part of an infertility evaluation, so it may not reflect the overall population.
The same 2025 study cited above for tobacco gets around some of these problems. Those researchers found, as with tobacco, that cannabis use had very large impacts on normal sperm morphology. Only about 8% of the sperm of cannabis users were morphologically normal, versus around 30% for non-smokers. Cannabis use also had a marginally significant impact on sperm concentration.
It would be helpful to have more data here — a large sample size and possibly more information on other behaviors men are engaging in. Ideally, we would have a randomized trial. Given the time frame of sperm production, one could take a set of cannabis users and randomize them into a period of abstention and observe their sperm before and after. This might be marginally easier than with tobacco smokers, given the lower level of physical addiction.
We do not yet have such a study, however. In the meantime, the data certainly suggests some negative impacts.
Impact of alcohol on sperm
There is a fairly robust literature showing that heavy alcohol consumption is associated with lower fertility. The exact mechanisms for this are unknown, but they may relate to the byproducts of ethanol consumption damaging sperm cells. Alcoholics are also more likely to report sexual dysfunction, which could contribute to lower fertility.
Many of the studies of this (here is an example) focus on extremely heavy drinkers — those who are consuming, say, a bottle of whiskey or brandy every day. In these individuals, all the elements of sperm quality — count, morphology, motility — appear to be compromised.
It is less clear how light or moderate alcohol consumption affects sperm. One study of Italian men being evaluated for infertility actually found slightly higher semen volume and sperm count in men drinking four to seven drinks per week versus one to three drinks per week. A systematic review concluded that there was less evidence of the impact of occasional drinking on sperm quality than there was on heavy drinking.
As in the case of cannabis, we do not have all the data we would want here. There is no strong guidance to point to a level of alcohol consumption that is “too high,” and we do not have large enough sample sizes to detect smaller impacts. What we can say is that heavy drinking is not good for fertility, and moderate or occasional drinking probably has limited effects.
An argument for routine sperm tracking
For all of these substances, it seems likely that usage impacts sperm health. However, the data isn’t conclusive in terms of how much it matters and how that varies across men. For some men, perhaps those with a very high baseline level of healthy sperm, this may not be an important driver of fertility. It may also be the case that these substances affect different men differently. We don’t completely know.
However, what’s great about sperm is that you do not have to idly wonder about this; it’s testable in your particular case.
If you are trying to conceive or planning to try, it may be a good idea to get a sperm health test. Your doctor can do this, and there are some (less precise) at-home options. If things look good with whatever your current behavior is, you can breathe easier. If things do not look good, you can adjust your behavior, wait two months, and test again. For couples who are trying to conceive, female cycle tracking is common. Sperm tracking should be, too.
The bottom line
- Cigarette smoking negatively impacts sperm. We don’t have direct evidence on sperm in non-smoking nicotine users. Although existing data points to negative effects, it’s still incomplete.
- The evidence is limited, but what we have consistently links cannabis use to poorer sperm quality.
- Heavy drinking clearly harms sperm quality, but moderate or occasional alcohol use has limited effects.
- The size of the impact of substance use varies across men. The best approach is simply to test your own sperm, adjust if needed, and check again.
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How far ahead of TTC should these behaviors be stopped if you are trying to maximize sperm health?
This is helpful, but can you define “heavy drinking,” “moderate drinking” and “occassional drinking” as referenced in this phrase? In terms of amount drunk in a single sitting and daily/weekly.
“heavy drinking is not good for fertility, and moderate or occasional drinking probably has limited effects.”