Study results show that use of oral hormone replacement therapy was associated with a 58% increased risk of venous thromboembolism, compared to no exposure.
Women take HRT to cope with menopause symptoms including depression, hot flushes and night sweats.
Taking HRT pills to cope with the menopause doubles the risk of unsafe blood clots, research has found. "However, the study should reassure women that blood clots are an uncommon complication of HRT, regardless of the preparation".
The Nottingham study aimed to provide clarity on the subject by identifying and comparing venous thromboembolism risks for all forms of HRT treatment used in the UK.
"These numbers are for the general population so if a woman is at an increased risk - due to cardiovascular disease, cancer or kidney disease, for example - these numbers will be much higher for her".
The researchers compared the treatment prescription records of all women who developed blood clots with those for a group of women who did not.
The researchers also took into account other potentially influencing factors, such as lifestyle, family history of blood clots and any underlying conditions linked to blood clots.
Tablets were associated with an extra nine cases in every 100,000 women.
Moreover, HRT tablets containing equine estrogen, including single and combined tablets, were consistently associated with higher risks than tablets containing synthetic oestrogen. Patches, creams and gels had no raised risk of clotting.
Dr Yana Vinogradova, of the University's School of Medicine, undertook the research. The team also included Professors Julia Hippisley-Cox and Carol Coupland.
"It has also confirmed that risks of thrombosis for patients using HRT treatments other than tablets is very low".
HRT patches have the lowest risk and should be first choice for older women, for whom blood clot risk is highest'.
Professor Helen Stokes-Lampard, chair of the Royal College of Global Positioning System, said that the study was interesting but could not prove that the HRT tablets had caused the blood clots, and added that it was important patients didn't panic or immediately stop taking HRT.
"Our findings are particularly important information for women, who require HRT treatment and are already at increased risk of developing blood clots".
Vinogradova, Y., Coupland, C., & Hippisley-Cox, J.
The latest findings on the hormone therapy, which replaces oestrogen lost naturally with ageing, come from a study of more than 470,000 women.