A large-scale clinical trial has concluded in Spain, with results raising concerns about the safety of one of the most widely used antiviral drugs. The focus was on valacyclovir, a medication commonly prescribed to treat the herpes simplex virus. This time, however, researchers examined its effects on patients in the early stages of Alzheimer’s disease who had herpes antibodies detected in their blood.
The experiment involved 120 volunteers divided into two equal groups. One group received valacyclovir in increasing doses, while the other was given a placebo. The study lasted 78 weeks, allowing specialists to closely monitor changes in the patients’ conditions and track even the slightest shifts in their cognitive abilities.
Unexpected results
Contrary to expectations, antiviral therapy brought no improvements. In fact, patients taking valacyclovir experienced a marked decline in memory and other cognitive functions compared to those who received a placebo. Statistical analysis confirmed the significance of these differences, even after adjusting for age, gender, and the participants’ genetic profiles.
At the same time, researchers did not observe changes in amyloid and tau protein levels—key biomarkers for Alzheimer’s disease. There were also no differences in hippocampal volume or cortical thickness between the two groups. According to patients’ self-assessments, their quality of life remained roughly the same regardless of the therapy.
Possible reasons
One of the hypotheses put forward by Spanish specialists is related to the potential neurotoxicity of valacyclovir. It is known that high doses of this drug can cause confusion, agitation, and even delirium. In this case, the patients took relatively high doses for an extended period, which, according to the researchers, could have led to mild but persistent disruptions in brain function.
Previously, the role of the herpes simplex virus in the development of dementia was actively debated in the scientific community. Some studies indicated a link between the infection and the risk of Alzheimer’s symptoms, while others refuted these findings. However, such large-scale and controlled trials of antiviral drugs in patients with early signs of the disease had not been conducted until now.
The debate continues
The results of the Spanish study have sparked a lively debate among neurologists and infectious disease specialists. Some believe the data call for a reassessment of how herpesvirus infections are treated in the elderly, particularly in patients already diagnosed with cognitive impairment. Others urge caution in interpreting the findings, citing the need for further research involving a larger sample of patients and longer follow-up periods.
Meanwhile, Spanish clinics have already begun revising their protocols for prescribing valacyclovir to dementia patients. Physicians now advise carefully weighing the potential risks and benefits, especially when considering long-term use of the drug.
What’s next?
For now, experts remain divided on whether the use of valacyclovir should be completely abandoned in patients with Alzheimer’s disease. Some suggest exploring alternative methods for preventing and treating herpesvirus infections to avoid worsening the progression of neurodegenerative diseases. In any case, the new data have already influenced treatment strategies and prompted a reassessment of medical care standards.
If you didn’t know, valacyclovir is an antiviral drug widely used to treat infections caused by the herpes simplex virus and shingles. In Spain, it is included in the list of essential medicines and is frequently prescribed to elderly patients. The drug’s manufacturer actively collaborates with research centers around the world, funding clinical trials and safety study programs for its products.
