Researchers from Columbia University Medical Center in New York have found that a group of drugs called JAK inhibitors can help increase scalp hair growth and encourage hair regrowth. These drugs tackle the activity of a family of enzymes called Janus kinase (JAK), which are found in the hair follicles. By inhibiting the JAK enzymes, the drugs seem to promote the hair follicle’s re-entry into the anagen growth phase of the human hair cycle, ultimately pushing new hair shafts up and out from the scalp.

Sources: AAAS, Science Advances "Pharmacologic inhibition of JAK-STAT signaling promotes hair growth."