Low doses of aspirin were only effective in preventing vascular events in patients weighing <70 kg, a recent study found. Researchers used individual patient data to analyze the modifying effects of bodyweight and height on the effects on low doses (≤100 mg) and higher doses (300‒325 mg or ≥500 mg) of aspirin in randomized trials of aspirin in primary prevention of cardiovascular (CV) events. They found:

• Low doses of aspirin (75‒100 mg) were only effective in preventing vascular events in patients weighing <70 kg.
• There was no benefit in 80% of men and nearly half of all women weighing ≥70 kg.
• Conversely, higher doses of aspirin were only effective in patients weighing ≥70 kg.
• Findings were similar in men and women, in people with diabetes, in trials of aspirin in secondary prevention, and in relation to height.
• Aspirin-mediated reductions in long-term risk of colorectal cancer were also weight dependent.