Drug use
Cocaine reduces sperm motility and may prevent fertilization. Cannabis leads to a lowered sperm count and an increase in abnormal sperm. Smoking just one joint lowers testosterone levels for up to 36 hours.
Many prescription and over-the-counter drugs can also negatively affect sperm production including anit-histamines and anti-depressants, so ask your GP or pharmacist for advice.
Smoking
Smoking has been shown to reduce both the sperm count and the sperm motility and has been shown statistically and clinically to damage sperm. Not only that but it also raises the likelihood that any child conceived will get some form of cancer, so stop now!
Alcohol
One heavy social drinking session can reduce your sperm count down for a short time, and regular bingeing can damage the tubes that carry semen, reduce sperm motility and increase the number of abnormal sperm cells. Alcohol has been statistically proven to damage sperm. Giving up alcohol for three to six months is often enough to restore greater fertility.
Coffee
Caffeine decreases sperm motility if drunk in excess, although one cup of coffee per day appears not to present any problems. Remember caffeine is present in chocolate, tea, fizzy drinks and many energy drinks as well.