New Delhi, Jul 2 (IANS): Excess smoking and use of other narcotic substances, including marijuana, can cause infertility in both males and females, doctors have said.

They said while cigarettes do not necessarily cause infertility, they can have an adverse effect on a couple's ability to conceive. The problem exists in men as much as in females, the doctors said.

"One should avoid using tobacco (cigarettes) and marijuana. They reduce fertility, especially by reducing sperm counts. Smoking damages sperm, making them less likely to fertilise eggs. The embryos they create are less likely to survive," said Nupur Gupta, associated with the Well Women Clinic.

According to Gupta, women who smoke tobacco, marijuana and several other narcotic products may have early menopause.

Studies have also revealed that compared to non-smokers, active smokers were 14 per cent more likely to be infertile and 26 per cent more likely to have early menopause.

World Health Organization (WHO) has stated that as of 2015, India with 12 per cent of world's tobacco users, has 108 million smokers.

Parbeen Mehta, a gynaecologist at Ram Manohar Lohia Hospital, said human sperm cells carry two tiny, highly charged proteins called protamine 1 and protamine 2 which are in a perfectly balanced one-to-one relationship.

"However, sperms of the smokers carry very little protamine, which makes them highly vulnerable to DNA damage," said Mehta.

She said passive smoking may also affect male fertility.

"Male smokers can suffer decreased sperm quality with lower mobility and it boots numbers of abnormally shaped sperms. Also, if one is a chain smoker then it might also decrease the sperm's ability to fertilise eggs," said Mehta.