An Alzheimer’s drug being tested modestly slowed the inevitable worsening of the disease, however with a risk of dangerous side effects for some, leaving researchers unclear on how much of a difference it makes.

Japanese drugmaker Eisai and its American partner Biogen announced in September that the drug ‘lecanemab’ appeared to work, reducing the rate of decline by 27%.

The latest data showed the drug slowed the advance of the brain disease in its early stage by around 5-months over the 18-month period of the study.  

However, about 16% of patients had two copies of a gene variant known to raise the risk of developing the brain disease, while 53% had one copy of another gene and 31% were non-carriers.

The U.S.Food and Drug Administration is scheduled to decide by January 6 whether to approve ‘lecanemab’ under its ”accelerated” review program, which requires proof a drug can impact a biomarker associated with a disease, such as reduction of the sticky deposits of a protein called amyloid beta in the brains of those with early Alzheimer’s.