How We Rate

We evaluate the available evidence on strategies to promote brain health and prevent dementia—such as FDA-approved drugs, herbal supplements, and vitamins—and summarize our findings in reports.

Some strategies are very promising, but have not yet been tested by rigorous scientific studies. Others have been tested but shown to have only a small effect on brain health. And a few have safety concerns that might outweigh any potential benefit. So, we rate the evidence, potential benefit, and safety. All ratings are determined by the neuroscientists of the Alzheimer’s Drug Discovery Foundation’s Aging & Alzheimer's Prevention Program and reviewed by our Clinical Advisory Board.

To rate the strength of scientific evidence, we consider many factors, including the type of study, its size and duration, the type of patients involved, the consistency of findings across studies, and possible conflicts of interest. We rate human clinical studies above preclinical studies done in animals or test tubes. Studies are also rated more highly if they directly examine the use of a treatment. For example, a study on vitamin intake is more applicable than a study on how vitamin levels vary naturally across individuals because low vitamin levels might be a consequence rather than a cause of the disease. These factors can increase or decrease the ratings, which follow the general guidelines below.

There is evidence from multiple randomized controlled trials or from a randomized trial in combination with a systematic review of observational studies, all in humans. A biological rationale for the treatment has been developed from preclinical studies.

Evidence includes at least one appropriately designed randomized controlled trial or a systematic review of observational studies, all in humans. A biological rationale for the treatment has been developed from preclinical studies.

There is some evidence on the use of the therapy from human studies (e.g., randomized trials, open or uncontrolled trials, or observational studies). A biological rationale for the treatment has been developed from preclinical studies.

Preclinical studies in animals and test tubes have evaluated its potential for biological effects, but there is no information on its effects on brain health in humans.

No human clinical studies have been conducted on brain health and no preclinical studies have developed a biological rationale for the treatment.

We rate the potential benefit to brain health using available evidence. Our ratings are based on the extent of the potential benefit, whether it is long- or short-term, and how useful the benefit is to daily life. For example, some treatments might potentially increase scores on cognitive tests but have no measurable effect on common work or life tasks. Because some of the most promising treatments have not yet been rigorously tested, we rate potential benefit separately from evidence.

Research suggests a clinically meaningful benefit for long-term brain health.

Research suggests a noticeable benefit to short-term brain health or a small benefit for long-term brain health.

Research suggests a small benefit to short-term or long-term brain health but the clinical evidence is uncertain (i.e., it is unlikely to be noticeable in daily life).

Research to-date suggests that benefit to brain health is unlikely.

No research evidence is available to estimate potential benefit to brain health.

The ratings reflect long-term use by a healthy adult at standard doses following the guidance of their physician. The safety of any treatment choice varies based on age, health status, genetics, medication use, and other variables.

Very low risk. Extensive clinical research suggests that side effects or adverse events are very rare or mild for most people. This research could include several high-quality long-term randomized trials or rigorous post-marketing surveillance of consumer use.

Low risk. Limited clinical research suggests that side effects or adverse events are rare or mild for most people. This research could include one or two high-quality long-term randomized trials, limited post-marketing surveillance of consumer use, or widespread consumer use that has not identified health risks yet have not been monitored for long-term use in scientific studies.

Moderate Risk. Extensive clinical research has raised concerns for significant side effects or adverse events. Or, the clinical research does not predict significant risks but is extremely limited with no long-term randomized trials or long-term widespread consumer use.

High risk. Clinical research indicates serious side effects or adverse events. Or, the clinical research is completely inadequate to gauge safety, with no relevant randomized trials and no reliable information from long-term consumer use.

No clinical research evidence or use by consumers/patients exists.