A new class of drug has been developed that promises to end the misery of menopausal hot flushes.
In an early trial, one experimental pill reduced hot flush episodes by almost 75% in just three days.
The severity of flushes was also cut by more than a third.
Participants in the trial were 37 women aged 40 to 62 who were suffering the effects of seven or more hot flushes per day.
The women were given the drug, code-named MLE4901, for one month and its effects were compared with taking a dummy pill.
Lead scientist Professor Waljit Dhillo, from Imperial College London, said: "We already knew this compound could be a game-changer for menopausal women, and get rid of three-quarters of their hot flushes in four weeks. But this new analysis confirms the beneficial effect is obtained very quickly - within just three days."
Due to side effects that might affect liver function, MLE4901 is not being taken forward into larger trials. But two very similar drugs have been developed that work in the same way without this problem, Prof Dhillo added. One is now undergoing trials in the US.
Hot flushes are a common symptom of the menopause, which occurs when a woman's oestrogen levels fall, typically at about 45 to 55 years of age.
For many women, flushes may be little more than an uncomfortable inconvenience, but for others they can result in sweat-drenched clothing and bed sheets, sleepless nights, and disrupted social and working lives.
The new compounds block the action of a brain chemical called neurokinin B (NKB). Previous research has suggested that NKB may trigger hot flushes by activating temperature control regions of the brain.
Study co-author Dr Julia Prague, also from Imperial College, said: "As NKB has many targets of action within the brain the potential for this drug class to really improve many of the symptoms of the menopause, such as hot flushes, difficulty sleeping, weight gain, and poor concentration, is huge.
"To see the lives of our participants change so dramatically and so quickly was so exciting, and suggests great promise for the future of this new type of treatment."
The scientists, whose findings are reported in the journal Menopause, hope the new drugs will provide a safer alternative to hormone replacement therapy (HRT).
Many women are unable to use HRT because of evidence that it can raise the risk of breast cancer and blood clots.