Texas is an employment at will state and you can be terminated for any reason or no reason at all in most circumstances. If they fired you for failing a drug test, you really don't have any recourse. Now, you do mention that it turned out to be a work injury - if you think the termination may have been for filing a worker's compensation claim, then you might have a retaliation claim.
If you are a member of a union or have a specific contract of employment, then you may have some additional rights. You should look into a consultation with an employment lawyer in your area who can go through all of the wrinkles of your factual circumstances and help you determine what rights you may have.
This answer is made available for educational purposes and is not intended to give you specific legal advice. I do not represent you and by using or participating in this site you understand that there is no attorney client relationship or privilege between you and me. This site should not be used as a substitute for legal advice from a retained, licensed attorney in your state who has reviewed your question and the surrounding facts in detail. I attempt to provide good, helpful information, but do NOT rely on anything I write - you should use my comments as a starting point for consulting an attorney you have retained to represent you regarding your specific legal and factual circumstances.
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