Is neem oil alright to use on my houseplants?

Yes! Apply neem oil early in the morning or at night when beneficial insects are dormant. This also protects the foliage from burning from the combination of sunlight and the oil. Keep in mind that it does take time for neem oil to work and you may need to reapply. Follow the directions on the bottle. Neem oil does have a strong smell so be mindful of that.