The liquid drops include small amounts of purified pollen, mold, dust mites and grasses.
Researchers at Johns Hopkins published their report in the latest edition of the JAMA.
The report is the largest study of its kind to evaluate the effectiveness of oral allergy drops against other therapies for reducing symptoms of sneezing, runny nose and wheezing.
They looked at over 63 studies regarding allergy drops (also called sublingual immunotherapy), involving a total of 5,131 participants, mostly in Europe.
Currently, allergy drops are not approved for use in the U.S.
The researchers say there's strong evidence in eight of 13 studies to suggest that drop therapy can reduce coughing, wheezing and tightness in the chest.
Compared to antihistamines and nasal steroid sprays, the researchers found that allergy drops produced a 40 percent decrease in symptoms, such as nasal congestion and runny nose.
According to senior study investigator Sandra Lin, M.D:
"Our findings are clear evidence that sublingual immunotherapy in the form of allergy drops are an effective potential treatment option for millions of Americans suffering from allergic asthma and allergic rhinoconjunctivitis,"
For many people, taking allergy drops is much more convenient than other forms of treatment, as they can be taken at home and avoid the need to have to make an appointment to visit to a doctor for an allergy shot.
Lin, an associate professor of otolaryngology-head and neck surgery at the Johns Hopkins University School of Medicine, said that up to 40 percent of the U.S. population suffer from either allergic asthma or allergic rhinitis (hay fever).
However, the authors stress that people who suffer from allergic rhinoconjunctivitis or allergic asthma should consider all the risks and benefits of allergy drops before deciding what treatment option they wish to take.
The study was funded by the U.S. Agency for Healthcare Research and Quality.
Written by Joseph Nordqvist