1)Before Knowing effect of Rahu In 1st house we have to know about Rahu and Tanu Bhav so you may read this
Tanu Bhav Base Of Your Horoscop—
2)So Rahu In 1st house Genraly effect your body constitutions,health,brain,Nature and behavior.
3)Body constitutions—–Rahu is a shadow planet so there is no definite constitutions in classic only mentain Rahu is just like saturan and Rahu behave like rashi lord where it is situated. So if we consider Rahu is same as saturan then native may have unfair in colour and tall in heights( Strongly recommended please consider rashi for better outcome).
4)Health—Rahu is natural Melific so Rahu In 1st may cause ill health.Rahu is a planet which shows hidden quality and 1st house belongs to upper body limbs(Head) so native may suffering hidden problem of upper body limbs. So it is seen native may suffering many disease such as way one is cure then other may attacks and native may wandering one to another doctors.1st house belongs to brain and nature so native may suffering from physiological problem.Some time Rahu In 1st may also give skin problem. Rahu In 1st house may also cause mouth and dental problem.Rahu is planet of Maya creation or imagination so Rahu In 1st may also cause Hysteria type problem.
5)Brain,Nature and behavior—
Rahu is Tamsic planet so in 1st house it is giving Tamsic brain.Rahu is a planet which have accelerating power and insight seeing capacity so Rahu In 1st house increasing your brain power. So native may have great imagination power and guess hidden matter . So native may be smart from nature and a great copying quality . They are fickle in nature so they are just change there behavior according to situation. Native may be false speaker but they speak such a way then nobody guess there false.Rahu is planet which give attachment regarding materialistic world so Rahu In 1st house make native to money minded so they are wealthy. Hiddness,Hype creator,explosive type Tempar belongs to Rahu so when Rahu occupy 1st house then native have such type nature.Rahu is planet which belongs to Maya so Rahu In 1st native may inclinations regarding Magician or mysteries activity or Jadu Tona.1st house is Tanu Bhav so 1st house Rahu give native to extremely mental capacity just like unguided missile when any other planet may guided Rahu then native may do any impossible work or get name or fame.