Doctors and patients have been at each other’s throats for decades over how to treat a little gland in the neck—and patients may be gaining ground.

The butterfly-shaped thyroid gland produces hormones that regulate virtually every system in the body. Not enough production of thyroid hormones, known has hypothyroidism, can cause fatigue, weight gain, depression and other metabolic and fertility problems. Too much, the less common hyperthyroidism, can cause heart palpitations, tremors and bone loss.

Because those symptoms can have several other causes, many doctors diagnose thyroid disorders mainly with blood tests. Many also rely on a single form of treatment for hypothyroidism, which has made the synthetic hormone levothyroxine (Synthroid and other brands) among the most prescribed medications in the world.

But a vocal group of patients say they haven’t gotten better on levothyroxine, though their blood tests have returned to normal. They’ve banded together online to share their frustrations and promote alternative therapies.

Some top endocrinologists are coming around to their view. Studies have confirmed that 5% to 15% of patients don’t get better on levothyroxine alone. Discoveries of gene variations may help explain why.