Official figures show that the death rate for women in their fifties and sixties, from accidental overdoses and suicides, was higher than that recorded for those in their twenties last year.
The death rate for females in their forties is also "significantly higher" than a few years ago and is close to overtaking the rate for those in their thirties.
Most drug poisoning deaths among women involved antidepressants but increasing numbers were caused by paracetamol or methadone.
Overall female drug misuse deaths increased slightly in 2011 while the number for males fell, the Office for National Statistics said.
Rosanna O'Connor, director of delivery at the National Treatment Agency for Substance Misuse, said: "These statistics tell us that fewer are dying from the most dangerous drugs, especially among younger people.
"This reflects official statistics showing declining drug use and falling demand for treatment among young people.
"It is the over-40s, typically in poor health from a lifetime's drug use, who are at greater risk of dying from overdose. For them, and all drug misusers, treatment remains the best defence against drug-related death."
In its annual report on drug poisoning deaths in England and Wales, taken from coroners' figures, the ONS said that in 2011 a total of 1,772 drug poisoning deaths were registered for men (a 6 per cent fall on 2010) and 880 for women (a 3 per cent rise). Most were down to accidental overdoses but almost half of deaths among women were suicides.
The mortality rate for drug poisoning among men is now at its lowest level since 1994 (63.8 deaths per million population) but among women the rate has "increased significantly" since 2007 to reach 29.9 deaths per million population in 2011.
Analysis showed that female victims of drugs are increasingly older, likely to be a result of Britain's ageing population in general as well as declining drug use among younger generations.
The ONS said: "In 2011 the mortality rate for females aged 40 to 49 was almost as high as for those aged 30 to 39, at 28.3 deaths per million population.
"The rate in 40 to 49-year-old females has continued to rise and was significantly higher than in 2007 (but not as high as the peak in 2008).
"The female mortality rate for 50 to 69-year-olds has increased steadily over the last couple of years and is now 14.4 deaths per million population - its highest level since records began in 1993.
"Moreover in 2011 for the first time the female mortality rate in this age group was higher than the rate for 20 to 29-year-olds (13.3 deaths per million population)."
Heroin remains the biggest killer among drug-taking men despite a sharp fall in recent years but antidepressants lead to the most drug deaths among women.
Deaths from the painkiller tramadol have increased markedly from just one in 1996 to 154 last year, as it has been prescribed more widely.
The number of deaths from barbiturates is rising, up from six in 2007 to 37 last year, despite fewer of the drugs being prescribed.
Deaths from use of the gas helium have also increased from two to 42 over the same period.
The ONS noted that almost all deaths from barbiturates and helium were suicides.