Does smoking weed affect sperm when trying to conceive?
It may. In a small Duke study, men who used cannabis at least weekly had changes in the chemical tags on their sperm DNA across hundreds of genes, and more THC meant bigger changes. Health Canada notes cannabis may affect sperm count and quality. The lead researcher advises stopping at least six months before trying to conceive.
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What the research found
In a small study at Duke University, researchers compared the sperm of 24 men who smoked cannabis at least weekly with that of non-users, and ran matching experiments in rats.
THC, the active part of cannabis, was linked to changes in DNA tags across hundreds of genes. Men with more THC in their urine had bigger changes. These tags are part of epigenetics: chemical marks that help switch genes up or down without changing the genetic letters, and sperm carry them into the egg.
What nobody knows yet is whether those changes reach a child, or whether they reverse after a man stops. Health Canada also notes that cannabis may affect sperm count and quality.
So the honest summary: the study was small, the effect on children is unknown, and the signal is clear enough that researchers advise caution.
Why a father's habits can matter at all
Half of your baby's DNA arrives in a single sperm. For a long time, that was thought to be the whole story. The newer idea is epigenetics: chemical tags and tiny RNA molecules that sperm carry into the egg, which help switch genes up or down without changing the genetic letters.
In people, this is early research. Scientists can measure the tags, but nobody has yet shown what they do to a child. Much of the striking evidence comes from animals. In one mouse study, males trained to fear a particular smell before conceiving had pups, and even grand-pups, that were more sensitive to that exact smell, including pups conceived by IVF who had never met their father.
The hopeful part runs through all of it: these tags seem to shift when a man's habits shift. In a small Danish study, sperm from men who had weight-loss surgery showed a dramatic remodeling of DNA tags afterwards. That's why stopping cannabis is worth doing even if you've used it for years. The batch being built after you stop is built under new conditions.
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Why six months, not three
Most of a father's preconception plan runs on a 90-day clock, because a new batch of sperm takes about 64 to 74 days to build. Cannabis is the exception.
The Duke study's lead researcher advised assuming the changes are there, and stopping cannabis at least six months before trying to conceive. That's longer than a single sperm cycle, so start sooner than the rest of the plan.
On a calendar: if you hope to start trying in September, the cannabis-free stretch starts in March.
Already trying? Stop now. Every new batch is built under the conditions you give it, and the sperm that count are the ones still being made. See how long sperm take to regenerate and, for food, a father's diet before conception.
If smoking is how you use it
If you smoke cannabis mixed with tobacco, or smoke cigarettes too, there's a second, clearer story. A 2016 meta-analysis of 20 studies and 5,865 men found smokers had lower sperm counts, poorer sperm movement and fewer normally shaped sperm, and heavier smokers fared worse.
Vaping isn't a free pass either. In a study of young men in Denmark, daily e-cigarette users had a total sperm count of about 91 million, compared with 147 million in non-users. The authors noted there weren't many daily vapers and many also smoked cigarettes.
After birth, smoke reaches the baby directly, so a smoke-free home matters long after conception. Quitting all of it together is simpler than quitting one piece at a time, and your doctor can help.
Cannabis and the pregnancy itself
For the person carrying the baby, the advice is firmer. Health Canada says there isn't enough research to identify a safe amount of cannabis to use during pregnancy or breastfeeding, and that it may affect how a child's brain develops.
Pregnancy often starts before a positive test, so stopping before you try protects those early weeks too. It's one more reason couples often quit together. The CDC says there is no known safe amount of alcohol in pregnancy either, so many couples clear out both at once and keep the home smoke-free.
Quitting as a team helps. Nobody is tempted by a stash in the house, and it turns “his habit” into a shared plan for the baby.
How to stop, practically
- Pick a date at least six months before you hope to start trying, and write it down.
- Tell your doctor. Ask, “Can you help me quit cannabis, smoking or vaping?” and ask about quit aids for smoking.
- Plan for the evenings. If cannabis is how you wind down, line up a replacement: a walk, exercise, a shower, a show with your partner.
- Protect your sleep. Aim for a regular bedtime; it's part of a father's 90-day plan anyway.
- Clear the rest of the plan at the same time: cut alcohol, move the laptop off your lap, skip hot tubs. See how long a man should stop drinking.
If stress or low mood is what cannabis was managing, say so to your doctor. About 1 in 10 fathers get depressed around a birth, and getting support early helps you and your family.
Do this
- Stop cannabis at least six months before you plan to start trying.
- Quit tobacco and vaping at the same time if you use them.
- Ask your doctor for help quitting, including quit aids for smoking.
- Plan a new evening wind-down habit before your stop date.
- Make the home cannabis-free and smoke-free for both of you.
When to ask your doctor
Check with your doctor or midwife first if…
- You use cannabis prescribed for a medical condition: talk to your prescriber before stopping or changing it.
- You use cannabis to manage anxiety, low mood or sleep problems: tell your doctor so you get support while you stop.
Call your doctor now if…
- You have thoughts of harming yourself: call or text 988 (US) now.
- Once your partner is pregnant and has bleeding, fluid leaking or fewer baby movements: call the doctor or 911 now.
This page is general information, not medical advice. Every pregnancy and every child is different. Ask your doctor, midwife or pediatrician before changing supplements, diet or care.
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People also ask
How long should a man stop smoking weed before trying to conceive?
The lead researcher of the Duke cannabis-and-sperm study advises stopping at least six months before trying. That's longer than the usual 90-day plan, because nobody yet knows how quickly the sperm DNA changes reverse.
Does weed lower sperm count?
Health Canada notes that cannabis may affect sperm count and quality. The Duke study looked at chemical tags on sperm DNA rather than count, and found changes across hundreds of genes in weekly users. Both point the same way: stop before trying.
Are edibles safer for sperm than smoking?
The Duke study didn't compare edibles with smoking. It linked THC itself to the sperm changes, with more THC in urine meaning bigger changes, so edibles aren't a known way around the problem. Smoking adds the separate, well-documented harms of smoke on sperm. The advice is to stop cannabis in any form.
Can my partner use cannabis while we're trying?
Health Canada says there's no known safe amount of cannabis in pregnancy or breastfeeding, and pregnancy often starts before a positive test. Quitting together while you try is the simplest approach.