And what is its life for one dose? I feel like this would be the most feasible cargo for the protection from it.
Solar radiation, like any other form of radiation, can be shielded against, and there are medications to relieve the symptoms and aid the organism in healing, but there is no direct cure.
Unlike diseases, where the cause is viruses or bacteria developing inside the body, and you need to combat these, stopping the spread before it can cause too much damage, radiation causes direct damage to human body cells - you stop the "spread" by shielding the body against the radiation, and you deal with the damage through normal healing process.
There are drugs developed, like Ex-Rad and Entolimod that aid against radiation by boosting natural healing mechanisms of the body - DNA repair, purging reactive substances that could cause more damage, activating immune response to protect damaged areas from developing infection, trigger improved healing response etc - but that is all just boosting the organism's natural defense and dealing with damage caused by irradiation; the healing process. The only way to prevent that damage though, is not to get irradiated in the first place.
In theory, one way to protect astronauts from radiation would be using a protein found in tardigrades: https://www.nature.com/articles/ncomms12808. In an experiment, human cells engineered to express this protein suffered less DNA damage from X-rays. But this is highly speculative: humans are not the same as human cell cultures, and that's not even getting into the ethical issues of genetic engineering humans. So it would be accurate to say that no drug exists that protects humans against radiation.